1. Field of the Invention
The present invention relates to automatic transmissions for automotive vehicles and more particularly to improvements in or relating to an arrangement of a band brake, a servomotor therefor, a control valve, etc. of an automatic transmission.
2. Description of the Prior Art
In one type of a prior art automatic transmission, a control valve for a gear shift control is installed in a lower side portion of a casing, in which casing a power transmitting mechanism consisting of planetary gear sets, clutches, band brakes, etc. is accomodated. A fluid pressure actuated piston of a servomotor for control of a band brake is also installed in the lower side portion of the casing. In another type of a prior art automatic transmission, the control valve and the servomotor piston are installed in the upper side portion of the casing.
In the prior art transmissions, an anchor pin is installed in the casing on the opposite side to the servomotor piston, i.e., the anchor pin is installed is the place where a circular sectional casing portion and a horizontal casing portion are joined to form a sharp angled recession, in which circular casing portion and horizontal casing portion the power transmitting mechanism and the control valve are respectively installed. Due to this, the work for adjustment of the clearance between the brake band and the brake drum through adjustment of the axial position of the anchor pin relative to the casing cannot be done with ease and efficiency. This is particularly true when the transmission is installed on the vehicle body since it becomes difficult for the operator not only to observe the anchor pin but to handle tools in a limited space.
In the above described prior art transmissions, the control valve and servomotor piston are arranged adjacent each other, i.e., arranged in the same side portion of the casing. Due to this, it is required to enlarge a particular casing portion so as to attain a space for installation of both the servomotor piston and the control valve. This causes increase in size of the transmission and restrictions in arrangement of the hydraulic circuit. In order to solve this problem, it is considered to arrange the control valve and servomotor piston in such a way as to be spaced vertically from each other. However, when this is the case, the prior art transmission of the first mentioned type is required to expand downwardly, thus reducing the ground clearance of the transmission. In case of the prior art transmission of the second mentioned type, the transmission expands upwardly, thus reducing the effective volume of the engine compartment.